Use this clever trick to see your iPhone's true signal strength

Luckily, there's a trick to reveal your iPhone's true signal
strength, and it takes less than a minute to enable.

First, you'll need to access a hidden app on your phone called
Field Test Mode. To do this, you'll need to open up your Phone
app and dial the following number, *3001#12345#* , including the
asterisks and hashtag, and tap "Call."

This opens up Field Test Mode,
which is mostly filled with menus of cell signal jargon that you
don't need to worry about. What you're interested in is the tiny
number in the upper left-hand corner of your iPhone
— likely hidden behind the text "Back to Phone" if
you're using iOS 8 or iOS 9 — which is your
iPhone's true signal strength.

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Here, for example, my old iPhone 5 that's still running iOS 7 is
showing my cell signal to be -59. To exit Field Test
Mode, you can simply tap the home button and you'll be brought
back to your iPhone's home screen, no harm done.

While that number can vary anywhere from -40 to -130, it will
always be negative, and the closer that number is to zero, the
better your cell signal,
according to OSX Daily. The best signal you can get
would be -40, and no signal at all would be -130.

If your iPhone is running iOS 8 or iOS 9 and you can't see
the number because of Apple's new "Back-to-last-app" feature that
creates a link to the last app you were using in the same corner
of your screen, don't worry. There's still another way to display
your true signal strength. This method allows
you to always have easy access to that number
without going through the hassle of dialing out to the Field Test
App, enabling your iPhone to display both numbers so you
just tap the signal dots in the future to check.

To enable this, return to your phone and
dial *3001#12345#* and tap "Call," like before.

You'll be brought to the Field Test App again, but instead
of using the home button to exit, hold down your iPhone's
power/sleep button until it shows the "Slide to power off" screen
and then hold the down your iPhone's home button, which will
force quit Field Test App.

You'll be back to your iPhone's homescreen, but this time
you should notice that your signal strength number has replaced
your signal strength dots.

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If you tap that number, you can switch between the two as
you see fit.

To undo any changes you made, simply repeat the steps to
get into Field Test Mode and tap the Home button to exit the app,
and everything will revert back to normal.